1. Field
Apparatuses and methods consistent with embodiments relate generally to graphene-polymer layered composites and methods of preparing the same, and more particularly, to graphene-polymer layered composites having low thermal conductivity and high electrical conductivity and methods of preparing the same.
2. Description of the Related Art
In solid materials, heat energy is often transferred by lattice vibration, that is, phonons. The transferring capability of heat energy is represented by thermal conductivity. Thermal conductivity is dependent on either a mean free path of a phonon, which is affected by a thermal capacity characteristic, interior defects, and interface characteristics of a material, or a phonon group velocity. A thermal conductivity characteristic is a unique characteristic of a material, and in the case of a metal having many free electrons, heat is transferred by charges and thus, thermal conductivity is as high as hundreds of watts per Kelvin-meter (W/mK). In the case of a soft material that has no crystallinity in a wide temperature range, such as an organic material, or an amorphous material, phonon transfer is not easy and thus, thermal conductivity is as low as from about 0.1 to about 0.3 W/mK.
To solve the energy-related problems that future generations are to face, solar cells, hydrogen cells, and thermoelectric energy are getting much attention and are being extensively researched. Among them, the reuse of heat energy, which is wasted by 60% or more, and an energy conversion technique using solar heat are considered to be an important technique to be obtained. Since heat energy is used by converting heat into electrical energy, a material used in this heat conversion system needs to have low thermal conductivity and high electrical conductivity.
Polymers, such as thermoplastics or thermosetting polymers, are an attractive material in terms of flexibility, costs, and processability. However, as a thermoelectric material, polymer is not attractive due to its very low electrical conductivity despite its low thermal conductivity. Recently, however, the possibility of a polymer as a thermoelectric material has been demonstrated after a composite including the polymer and a nano material, such as a carbon nanotube (CNT) having high electrical conductivity, was developed. In this case, however, charge hopping may occur among CNTs in a CNT network and thus, there is a limit in improving electrical conductivity of the polymer.